Recently various kinds of radio telephones have been developed. One of these is generally referred to as a mobile radio telephone. The mobile radio telephone, which may be mounted in a car, a train, a ship, an airplane or the like, comprises a transceiver unit with an antenna and telephone unit including a handset and a base unit. These units are physically separated and are connected by signal lines to one another. The transceiver receives power from the battery normally used with the vehicle.
Another kind of radio telephone may be referred to as a portable telephone. Portable telephones may be further divided into two groups: a transportable type and a handheld type. In the transportable type of portable radio telephone, a transceiver unit is combined into a main unit of a telephone unit and an antenna is attached to the main unit; consequently a user may carry the transportable telephone wherever the user goes. In the handheld type, all components are compacted into one unit which may be held in the user's hand. Like the mobile units discussed above, these radio telephones also receive power from a battery. Differentiated from the kinds of radio telephone mentioned above, there is yet a further kind of radio telephone, namely a cordless telephone. The cordless telephone has one or more base units connected to one or more land lines and one or more handheld units. The handheld unit communicates with another telephone apparatus by establishing a radio channel with the base unit. This handheld unit also receives power from a battery.
Generally, it is desirable to reduce power consumption in a radio telephone since the battery installed therein or in the vehicle has a limited power capacity.
In prior art radio telephones, both a reception section and transmission section receives power after the main power switch is turned on whether or not the transmission section actually transmits any signals. Accordingly, an inordinate amount of power is consumed.
Most radio telephone systems include a modulator section and a power amplifier section. Any attempt to conserve power by supplying power to these section only when transmission is desired would have an adverse effect on the system. If the modulator modulates the desired signals before locking onto the appropriate frequencies, unwanted radio waves or spurious radiation will be produced.